Pumps for filtration systems have a number of conventional components. The pump drive system includes a motor which is connected through bearings to a drive shaft which, in turn, is joined by a coupling to an impeller shaft. The impeller shaft has impellers or blades mounted thereon. A discharge head is provided upon which the motor is mounted and through which the drive shaft and impeller shaft pass. Surrounding the impeller shaft and connected to an inlet in the discharge head is an impeller housing. Bearings are interposed between the impeller shaft and the impeller housing to provide support to the impeller shaft. The pump is mounted relative to a container or tank containing a fluid such as machine tool coolant.
The motor drives the drive shaft which, in turn, drives the impeller shaft. The impellers rotating with the impeller shaft force fluid through the impeller housing, into the inlet of the discharge head and out a discharge outlet or tube to apparatus such as machine tools.
These filtration pumps ideally should be inexpensive to manufacture and should be reliable having a long operating life. However, conventional pumps for filtration systems have a number of shortcomings which adversely effect the cost of manufacture and their reliability.
One source of manufacturing expense, which also relates to the reliability of a pump, is the need to use oversized bearings in the pump motor. Typically, the motor has bearings which provide axial and lateral support to the drive shaft. The drive shaft is subject to large axial loads due to the fluid being pumped interacting with the impellers on the impeller shaft. The force of the fluid acting upon the impellers pushes axially downward upon the impeller shaft which then pulls downwardly on the coupling and attached drive shaft. To prevent premature failure of the motor, the bearings need to be sufficiently large to withstand this axial loading. However, the use of oversized bearings increases the cost of manufacturing the motor, and accordingly, the overall cost of the pump.
Another component of the pump which may induce premature failure is the coupling joining together the drive and impeller shafts. Traditionally, couplings are multi-piece assemblies having numerous components. If these combined components are eccentric, or not radially well balanced, the couplings can introduce unwanted radial loads and vibrations to the drive system during rotation of the drive and impeller shafts.
A third shortcoming is fatigue failure of parts related to high stress in components of the drive system, including the motor, the drive shaft, the coupling and the impeller shaft. These components are generally quite large and stiff. If axial or other misalignment occurs during their assembly, such as those due to manufacturing tolerances, tightening and forcing these components together can create large stresses and loads in the drive system.
For example, while ideally components of the drive system are perfectly coaxially aligned with one another, in reality, they cannot be practically manufactured in this manner. The more out of coaxial alignment the shafts are with respect to one another, generally the greater the loads transferred to the bearings from the shafts. Therefore, there is a need for a relief mechanism which will deform to accommodate misalignment without creating large loads or stresses in the drive system.
Another mode of pump failure is the burning out of motors. If the fluid or coolant being pumped migrates into the lubrication system of an electric motor, lubricants, which normally serve as insulators, can become electrically conductive and short out the motor. Or else, the lubricating properties of the bearings may become diminished resulting in increased frictional degradation of moving parts within the motor. Therefore, a need exists for a reliable seal system or assembly in a pump which prevents the migration of pumped fluid into the motor.